Preparation And Properties Of Ti₃SiC₂ And Its Composites Joined Lanthanum Chromite Ceramics

LaCrO₃ ceramics are a kind of excellent performance chalcogenide functional ceramics with good electrical and thermal conductivity,which are widely used in solid fuel cells and high-temperature heating elements,etc.However,their brittleness is too high leading to their poor processability,making it difficult to directly process large and complex parts,so the use of ceramic joining technology to prepare large and complex-shaped LaCrO₃ components or to repair them helps to promote the practicality and engineering of lanthanum chromate ceramic materials.In this paper,Ti₃Si C₂ ceramics and Ti₃Si C₂-LaCrO₃,LaCrO₃/Ti₃Si C₂/LaCrO₃,Ti₃Si C₂-LaCrO₃/Ti₃Si C₂/Ti₃Si C₂-LaCrO₃ composite ceramics were prepared by using discharge plasma technology,and the microscopic morphology and composition of the material phases were analyzed by SEM and XRD.The effects of different sintering temperatures on the mechanical properties of the materials were investigated.Pure Ti₃Si C₂ ceramics were prepared at 1350～1400℃.The Ti₃Si C₂ ceramics prepared at 1400℃had the highest density of 96.36%and the fracture toughness of 8.56 MPa·m^1/2.The Ti₃Si C₂-LaCrO₃（molar ratio 1:1）composite ceramic has the highest density of 91.95%at 1300℃,and has high microhardness and fracture toughness of 7.51 GPa and 2.33 MPa·m^1/2,respectively.The relative density of LaCrO₃/Ti₃Si C₂/LaCrO₃ layered ceramics can reach 99.26%after calcination at 1400℃,and it has high microhardness.The Ti₃Si C₂-LaCrO₃/Ti₃Si C₂/Ti₃Si C₂-LaCrO₃ gradient ceramics calcined at 1500℃have a high density of 96.79%and a high microhardness.Ti₃Si C₂ and its composites were used as the interlayer to connect lanthanum chromate.The bonding strength was tested by universal mechanical testing machine.The joints were analyzed by means of SEM,EDS and XRD.The effects of different bonding temperatures and interlayer thickness on the strength were studied.The results show that when Ti₃Si C₂ is used as the interlayer,the highest bonding strength of 58 MPa is obtained when the bonding temperature is 1350°C and the interlayer thickness is 150μm.When Ti₃Si C₂-LaCrO₃（molar ratio 1:1）was used as the interlayer,the highest bonding strength of 68 MPa was obtained when the bonding temperature was 1400℃and the thickness of the interlayer was 600μm.When LaCrO₃/Ti₃Si C₂/LaCrO₃ layered ceramic is used as the interlayer,the highest bonding strength of 65 MPa is obtained when the bonding temperature is 1400℃and the total thickness of the interlayer is 300μm.When Ti₃Si C₂-LaCrO₃/Ti₃Si C₂/Ti₃Si C₂-LaCrO₃gradient ceramic was used as the interlayer,the highest bonding strength of 77 MPa was obtained when the bonding temperature was 1400℃and the total thickness of the interlayer was 300μm.Composite materials are more conducive to alleviating residual thermal stress than single-phase materials,and gradient materials are more conducive to improving connection strength than layered materials.The connection mechanism of the four intermediate layers to achieve high connection performance is mainly reaction connection,including diffusion connection and mechanical bonding.